Carcinomas of the anal canal and anal margin differ in their expression of cadherin, cytokeratins and p53.

Carcinomas of the anus are subdivided into those of the anal canal and those of the anal margin. It has been postulated that the various types of tumours of the anal canal represent a spectrum of differentiation rather than tumours of a separate origin. We compared the expression of Pan-cadherin, cytokeratins (CKs) 5/6, 7, 13, 18 and 19, p53 and MIB-1 in 17 cases of carcinoma of the anal canal and 5 cases of carcinoma of the anal margin. Expression of Pan-cadherin was decreased in 70% of carcinomas of the anal canal but preserved in all five carcinomas of the anal margin. Most of the carcinomas of the anal canal expressed all of the CKs studied. Carcinomas of the anal margin showed expression of CK 5/6 and CK 13, whereas CK7, CK18 and CK19 were rarely expressed. Loss of expression of CK 18 and 19, but not CK 7, is a marker of dedifferentiation in anal canal carcinoma. Of the carcinomas of the anal canal and anal margin, 46% and 80%, respectively, expressed p53. The immunhistochemical findings support the opinion that the various subtypes of carcinoma of the anal canal represent variants in differentiation of squamous cell carcinomas of the anal canal. They confirm the separate histogenetic origin of tumours from the anal canal and anal margin.